President Petro O. Poroshenko of Ukraine must swallow a bitter pill: The pact will force him to make concessions that will cement recent gains made by the pro-Russian separatist forces in southeastern Ukraine.

Here is a look at what the agreement does and does not resolve.

Can the cease-fire hold?

A cease-fire negotiated in September in Minsk failed. But the participation of Mr. Putin, Mr. Poroshenko and the leaders of Germany and France increase the likelihood that this agreement might hold.

Under Thursday’s deal, both sides must stop firing on each other at midnight on Saturday. That leaves 48 hours during which both sides may try to claim additional territory. The fiercest fighting will probably continue near Debaltseve, an important rail junction held by Ukrainian forces that the separatists claim to have surrounded. The Organization for Security and Cooperation in Europe is to monitor the cease-fire, but it cannot enforce it.

Where will the new dividing lines be?

The situation on the ground favors the separatists. Ukrainian officials have said that the rebels gained control over more than 500 square kilometers, or almost 200 square miles, of additional territory since the September cease-fire deal.

Under the new agreement, both sides are required to withdraw heavy artillery to create a 30-mile demilitarized buffer zone. But the agreement does not explicitly demarcate the line. Ukraine is required to withdraw from the “current front lines,” which may change by Saturday. Separatist forces are supposed to withdraw behind the September line.

What about Ukraine’s border with Russia?

Under the new agreement, Ukraine will regain control of its border with Russia by the end of 2015 if the government makes political concessions, including the adoption of constitutional amendments to decentralize power.

Mr. Poroshenko must sell those reforms to a wartime Parliament in Kiev that might see this agreement as a capitulation and scuttle the deal.

What about the humanitarian situation?

The government in Kiev agreed to resume paying pensions and other social benefits to residents of southeastern Ukraine, a significant victory for Moscow, which has accused Mr. Poroshenko of levying an “economic blockade.” The return of social benefits will aid residents in combat zones and bolster the standing of the rebel governments while further depleting Ukraine’s budget.

What about Ukraine’s aspirations to join NATO and the European Union?

Moscow has demanded assurances that Kiev will not join the European Union or NATO. Thursday's agreement did not allow for rebels to have their own foreign policy, but the political concessions the Ukrainian government must make give the separatists — and Moscow — leverage. Plus, further integration with Europe may be difficult under current political and economic conditions in Ukraine.

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The leaders of Russia, Ukraine, Germany and France, the main players in the cease-fire negotiations in Minsk, discuss the talks.CreditCreditPool photo by Tatyana Zenkovich

What about Crimea?

Crimea, the peninsula annexed by Russia from Ukraine last March, was not addressed in the agreement.

Are there other conditions?

Kiev promised to grant amnesty to fighters in the southeast. Illegal militias (both pro-Ukrainian and separatist forces) are to disband, and foreign mercenaries are to leave the country. These provisions were included in the previous agreement, but were never enforced. “All prisoners of war are to be exchanged. Mr. Poroshenko has called for the release of Nadiya V. Savchenko, a Ukrainian pilot, but she is being held in Moscow on criminal charges.

Who is going to enforce this?

The O.S.C.E. is to monitor the cease-fire and new local elections to be held in rebel territory before the end of the year. France, Germany, Russia and Ukraine are also required to form working groups that will meet regularly to monitor the agreement. Ultimately there are no provisions for enforcement. The agreement will hold only if both sides stand by it.